Asphalt composition containing polyethylene



United States. Patent ASPHALT COMPOSITION CONTAINING POLYETHYLEN E Clarence H. Thayer, Wallingford, Pa., assignor to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey N0 Drawing. Application July 13, 1956 Serial No. 597,598

4 Claims. Cl. 260-285 penetration at 392 F. by the penetration at 77 F. and

multiplying by 100. The greater the penetration ratio, the less hardening the asphalt undergoes upon cooling, greater penetrations indicating a softer asphalt and vice versa.

It is not uncommon for users of asphalt to specify a minimum penetration ratio. Asphalts as ordinarily produced in petroleum refining frequently have penetration ratios which are somewhat below such minimum specifications, and it is frequently diffieult to obtain a penetration ratio which is sufiiciently higher than that ordinarily obtained to meetthe specification. Often the penetration ratio of an asphalt produced by ordinary methods is only 1, 2 or 3 points lower than the specification, but it is difficult to raise the penetration ratio sufliciently to meet the specification.

According to the present invention, asphalts having increased penetration ratio are obtained by adding to an asphalt having penetration at 77 F. within the approximate range from 60 to 300, a small amount of polyethylene having average molecular weight within the approximate range from 500 to 12,000, preferably Within the approximate range from 1000 to 9000, more preferably 1000 to 5000.

It is known in the art to employ polyethylene having average molecular weight of 10,000 or higher in asphalt I compositions to reduce the brittleness of the asphalt. Such reduction of brittleness, however, is necessary only in the case of hard asphalts, e. g. those having softening points (A. S. T. D3626) above 75 C. and penetrations at 77 F. (A. S. T. M. DS-ZS) less than 50. In the case of other asphalts, e. g. those having softening points lower than about 70 C. and penetrations at 77 F. of at least about 60, reduction of brittleness is generally unnecessary, since the asphalt is sufficiently nonbrittle in the absence of an additive such as polyethylene.

The present invention involves the use of polyethylene to increase penetration ratio of asphalts having penetration at 77 F. within the approximate range from 60 to 300, and preferably within the approximate range from 80 to 120; these penetrations refer to the asphalt prior to addition of polyethylene. The asphalts preferably have ring and ball softening points, prior to addition of polyethylone, within the approximate range from 10 C. to 70 C. (40 F. to 158 F), and more preferably within the approximate range from 30 C. to C. (86 F. to 122 F.).

With asphalts as described in the preceding paragraph, addition of polyethylene is generally unnecessary or ineffective for reducing brittleness of the asphalt. Such addi- 2,871,212 Patented Jan. 27, 1959 tion usually affects, however, the penetration at 77 F. and raises the penetration ratio. In the prior art, by way of contrast, use of polyethylene to reduce brittleness of hard asphalts is indicated not to affect the penetration at 77 F and there is no indication that the penetration ratio is raised.

The amount of polyethylene which is employed according to the invention is a minor amount sufficient to raise the penetration ratio of the asphalt. Generally, the amount is less than 25 weight percent based on the asphalt-additive mixture. Preferably the amount is Within the approximate range from 0.1 to 4 weight percent, and more preferably within the approximate range from 0.25 to 1.5 weight percent. 1

The molecular weight of the polyethylene employed should not be substantially greater than 12,000. As the molecular weight increases for example to 8000, the beneficial effect on penetration ratio decreases, and when the molecular weight is too high, no benefit in penetration is obtained. Preferred specific gravities of polyethylene for use according to the invention are those within the approximate range from 0.85 to 0.93 at 20 C., though polyethylenes having molecular weight outside that range can also be employed.

The polyethylene which is employed according to the invention can be prepared by any suitable known method for polymerization of ethylene to produce polymers within the indicated molecular weight range. Various processes for producing polyethylene are well known in the art, and any of the known processes can be employed to produce the additive according to the invention.

Any suitable method can be employed for incorporating polyethylene in asphalt according to the invention. One suitable method involves agitation of a mixture of polyethylene and asphalt at an elevated temperature, e. g. within the approximate range from 300 F. to 600 F.

The following examples illustrate the invention:

Example I A vacuum reduced asphalt was prepared from Kuwait crude by standard vacuum distillation technique, to obtain an asphalt constituting an 18 to 20% bottoms fraction of the crude. The asphalt had a ring and ball softening point of 107 F., ductility of 105, flash point 640 F., fire point 720 F., Saybolt Fnrol viscosity at 210 F. of 1343 seconds, Saybolt Furol viscosity at 250 F. of 332 seconds, specific gravity at 77 F. of 1.029. A series of tests were made in which 0.5 weight percent'of polyethylene having specific gravity of about 0.92 at 20 C. and average molecular weight of about 1600'was added to the asphalt by agitation for 10 minutes at a temperature of 400 F. The following table shows the penetrations at 77 F. and 392 F. and the penetration ratio for the base asphalt and the asphalt containing 0.5% polyethylene. The penetrations were determined by standard A. S. T. M. methods, employing a gram weight applied for 5 seconds in the determination at 77 F., and a 200 gram weight applied for 60seconds in the 392 F. determination. The penetrations given for the base asphalt are averages of 9 different runs, and those given for the asphalt containing polyethylene are averages of 18 different runs.

The above table shows that 0.5% polyethylene having average molecular weight of about 1600 produces an increase in penetration ratio of 2.6 points. Such increase is highly beneficial in producing asphalt which will meet penetration ratio specifications, from asphalts which as ordinarily produced are somewhat below the penetration ratio specifications.

The penetration at 39.2 F. is slightly lower on the average for the asphalt which contains polyethylene than for the base asphalt, thus indicating slight hardening of the asphalt by use of the additive. The extent of hardening is considerably greater at 77 E, which accounts for the increase in penetration ratio, the latter being the ratio of penetration at 392 F. to penetration at 77 F.

In view of the hardening which takes place as a result of addition of the polyethylene of this example it is desirable to employ such polyethylene in an asphalt which has a somewhat higher 77 F. penetration initially than that which is desired in the final product. In this way, addition of polyethylene reduces the penetration to the desired level and also produces an advantageous increase in the penetration ratio. With lower molecular weight polyethylenes than those employed in this example, the increase in penetration ratio may be obtained without a decrease in penetration.

Example 11 In similar experiments to those described in Example I, but using one percent of three difierent polyethylenes having different average molecular weights, the following results were obtained:

Molecular weight of polyethylene: Increase in pen. ratio These results show that as molecular weights increase to 8000 and higher, the effect of the polyethylene on the penetration ratio decreases, till at 13,000 molecular weight, there is no beneficial effect on penetration ratio.

Example 111 Molecular weight of polyethylene: Increase in pen. ratio 1,600 8 These results show a molecular weight efiect generally similar to that shown in Example II for a different asphalt.

Average molecular weights, as referred to herein, are determined by measuring the kinematic viscosity in centistokes at 220 F. of a 5 weight percent solution of polyethylene in paraflin wax having melting point of 133- 135 F., and calculating the molecular Weight from the formula, W =721V 1924, where W is the average molecular weight, and V is the 220 F. viscosity in centistokes.

Where penetrations at 77 F. are referred to herein, the manner of determination is by test method A. S. T. M. D525 using a 100 gram weight applied for 5 seconds. Where penetrations at 39.2" F. are referred to, the manner of determination is by similar procedure using a 200 gram weight applied for seconds.

The invention claimed is:

1. As a new composition of matter, asphalt having penetration at 77 F., prior to addition of polyethylene, within the approximate range from 60 to 300 and containing an amount less than 25 weight percent and suflicient to raise the penetration ratio of said asphalt, of polyethylene having average molecular weight within the approximate range from 500 to 12,000, said penetration ratio being determined by dividing the penetration at 392 F. by the penetration at 77 F. and multiplying by 100.

2. Composition according to claim 1 wherein said molecular weight is within the approximate range from 1000 to 9000.

3. Composition according to claim 1 wherein the weight percent of polyethylene is within the approximate range from 0.1 to 4.0 weight percent based on the sum of the Weights of polyethylene and asphalt.

4. Composition according to claim 1 wherein said penetration is within the approximate range from 80 to 120.

References Cited in the file of this patent UNITED STATES PATENTS 2,475,699 Derksen July 12, 1949 2,610,956 Derksen et al Sept. 16, 1952 2,690,418 Young et al. Sept. 28, 1954 OTHER REFERENCES High Polymers, volume 11, entitled Polyethylene, by Rafi et 211., published 1956 by Interscience Publishers, Inc., page 226.

Asphalts and Allied Substances, by Abraham, 5th edition, volume 1, page 522. 

1. AS A NEW COMPOSITION OF MATTER, ASPHALT HAVING PENETRATION AT 77*F., PRIOR TO ADDITION OF POLYETHYLENE, WITHIN THE APPROXIMATE RANGE FROM 60 TO 300 AND CONTAINING AN AMOUNT LESS THAN 25 WEIGHT PERCENT AND SUFFICIENT TO RAISE THE PENETRATION RATIO OF SAID ASPHALT, OF POLYETHYLENE HAVING AVERAGE MOLECULAR WEIGHT WITHIN THE APPROXIMATELY RANGE FROM 500 TO 12,000, SAID PENETRATION RATIO BEING DETERMINED BY DIVIDING THE PENETRATION AT 39.2*F. BY THE PENETRATION AT 77*F. AND MULTIPLYING BY
 100. 